High frequency transistor



Oct 31, 1961 D. Q. FULLER HIGH FREQUENCY TRANSISTOR Filed Sept. 5, 1958Inventor Dennis Q Fu//er B MM J ttorneys- 3,007,091 HIGH FREQUENCYTRANSISTQR Dennis Q. Fuller, Cambridge, England, assignor to llyeLimited, Cambridge, England, a British company Filed Sept. 5, 1958, Ser.No. 759,195 Claims priority, application Great Britain Sept. 10, 1957 4Claims. (Cl. 317-235) The present invention relates to transistors,particularly PNIP, NPIN or graded base transistors, and othertransistors having a built-in accelerating field region in the base.

Such transistors normally have a washer-like base connection electrodeon that face of the base wafer which carries the emitter. According tothis invention an additional electrode is connected to the opposite faceof the base wafer so that a biasing potential can be applied between thebase electrode and additional electrode with such polarity that theminority carriers are accelerated towards the collector.

According to a feature of the invention, the additional electrode isbrought as near as practicable to the actual transistor junction withoutcoming into direct electrical contact therewith, the electrode being in'close electrical contact with the base itself over the intrinsicregion.

Referring to the accompanying drawing, which shows a PNIP transistoraccording to the invention, E is the emitter and C the collector onopposite faces of the base wafer B. 1 is the usual base electrode and 2is an additional washer-like accelerating or hook electrode on theopposite face of the base. The electrode 2 may include a metal film 2aevaporated on to the surface of the base and reaching almost to thecollector junction but not over it. A voltage V is applied across theelectrodes 1 and 2, with the positive pole connected to the electrode 1.This voltage will accelerate carriers towards the collector. The voltageV can be much greater than the voltage V, applied to the collector.

When V is large, a space charge (i.e. trapped holes) will be creatednear the collector junction, and a signal current S applied to theaccelerating electrode 2 will control the current to the collector fromthe immediate vicinity of the junction, thus enabling very highfrequency response.

Sta atent f It may be advantageous to create a slightly P type re- 4gion, labelled P1 in the drawing, in the area under the collectorelectrode and extending to electrode 2. Such a region provides anarea ofsubstantial conductivity so as to encourage current to flow over aslarge a portion of the transistor as possible as a. result of theinfluence of the potential V.

It is possible that under some conditions an alpha (grounded baseamplification) greater than unity can be produced, thus combining themerits of point contact with the reliability of junction transistors.This effect could be applied to correcting beta fall-off of any junctiontransistor.

3,dd7,9l ?atented ct. 31, 1961 The invention provides a junctiontransistor with an accelerating field in the base region. This willensure an improved frequency performance and current gaincharacteristics. It also enables a signal to be impressed on it via theadditional electrode 2, thereby enabling the transistor to be used as amixing device.

I claim:

1. A transistor comprising a base wafer of semiconductor material whoseconductivity characteristic varies from one face to the other face andincluding an intrinsic region adjacent the other face, an emitter onsaid one face of the wafer, a collector on the opposite face of thewafer in the intrinsic region, a first annular base electrode attachedto said one face of the wafer and surrounding the emitter, a secondannular base electrode attached to the other face of the wafer andsurrounding the collector, and a metal film extending over the otherface from the second base electrode to closely adjacent the collectorwithout coming into direct electrical contact therewith.

2. A transistor comprising a base wafer of semiconductor material whoseconductivity characteristic varies from one face to the other face, anemitter in the centre of said one face of the wafer, a collector in thecentre of said other face of the wafer and opposite said emitter, afirst annular base electrode attached to one face of the wafer andsurrounding the emitter and a second annular base electrode attached tothe other face of the wafer and closely surrounding the collector andincluding a metal layer extending to closely adjacent the collectorwithout coming into direct electrical contact therewith.

3. A transistor comprising a base wafer of semiconductor material havingan N-type region adjacent one face and an intrinsic region adjacent theother face, a P-type emitter on said one face of the wafer, a P-typecollector on the opposite face of the wafer in the intrinsic region, afirst annular base electrode attached to one face of the wafer andsurrounding the emitter, and a second annular base electrode attached tothe other face of the wafer and closely surrounding the collector andincluding a metal layer extending to closely adjacent the collectorwithout coming into direct electrical contact therewith.

4. A transistor as claimed in claim 3, in which a P-type conductiveregion is formed in the intrinsic region in the area under the collectorand extending to the second annular base electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,801,348 Pankove July 30, 1957 2,842,668 Rutz July 8, 1958 2,847,583Lin Aug. 12, 1958 2,851,594 Herold Sept. 9, 1958 2,857,527 Pankove Oct.21, 1958 2,900,531 Wallrnark Aug. 18, 1959

